Multicenter collaboration to reduce the risks inherent in allogeneic hematopoietic cell transplantation (HCT) is essential to dampen the dangers of regimen toxicity, infection, transfusion dependence, graft vs. host disease (GVHD) and malignant relapse. Ongoing efforts to address all these risks have been a focus of Network participation for investigators at the University of Minnesota. Our commitment to the Network has included participation as Steering Committee chair, national PI of four protocols, leading the first four Network publications and committing institutional resources to develop and successfully execute Network trials. Because umbilical cord blood (UCB) transplantation is still limited by delayed or failed engraftment, we initiated studies to augment the homing and hematopoietic recovery of UCB grafts based on preclinical data suggesting that complement fragment C3a can accomplish these goals. An ongoing University of Minnesota phase 1 trial testing C3a priming of one of a pair of UCB units to augment engraftment and enhance predominance of the primed unit provides the clinical background for a proposed multicenter phase 11. We propose a protocol testing whether C3a priming of one UCB unit can increase the likelihood of that unit's predominance as the engrafting hematopoietic source; can augment and accelerate multilineage hematopoietic recovery; and can enhance immune reconstitution thereby lessening risks of infection without excess graft vs. host disease. We offer our continued commitment to the Network's success in developing new protocols, identifying patients suitable for Network trial enrollment and performing protocol specific procedures. We will try to exceed the Network's standards in our commitment to enhance multicenter trial success and advance scientific progress within the Network. Multicenter collaborative trials are essential to formally test new ways to enhance the safety of allotransplantation and improve outcomes for our patients.